The present invention relates to stator core assemblies for rotating machines of the type whose stator is composed of a plurality of stator core members, or punchings, secured together in a stack by a plurality of bolts distributed around the circumference of the assembly and extending parallel to the machine axis of rotation.
The stator core members are clamped together by the bolts and it is important, particularly during the operation of large generators, to maintain the force with which the stator members are clamped together at a specified level. It is impossible to maintain a substantially constant clamping force in known assemblies because the temperature of such a machine varies considerably from starting to normal operating temperature and suitable bolt materials have a substantially higher coefficient of thermal expansion than do the laminated silicon steel punchings commonly used to form the core stack. As a result, the clamping force imposed on the stack either becomes too low during operation or must be set higher than desired during manufacture. In the former case, the desired level of core tightness is not maintained; in the latter case more stringent strength requirements are imposed on the structural members of the stator core.
Moreover, since such a stator core assembly is frequently required to be capable of operating at low temperature, the assembly must be capable of supporting loads greater than that established during manufacture.
Thus, known stator core assemblies must either be overbuilt to support higher clamping loads than required for proper operation, or be allowed to operate without optimum tightness.